Radio reception system



Jan. 21, 1941.

H. R. BUTLER RADIO RECEPTION SYSTEI Filed Jan. 28, 1959 Examiner I .LE:.- l

75 RADIO FREQUENCY 7 AMPLIFIER "5i, [a 1 RADIO RECENER 19 lab I 25MODLLATION LOCAL SOURCE TRANSMITTER [20c TRANSMITTER /}'Z A 7 iFREQUENCY 1 MJLTIPLIER E 35 I. E .1. E... E E .1. 2 E 7 /3 /5Z, n)

AMPLIFIER AMPLIFIER TRANSFORM LOCAL LOCAL TRANSMITTER TRANSMflILh 784 mtE m 35 2 4 I 44 i7 45 4 -sm%1 w l E INIFENTOR Y Ham- R. Huflar TOINDIVIDUAL RECEIVERS ATTOR N EY Patented Jan. 21, 1941 UNITED STATESExaminer PATENT OFFICE RADIO RECEPTIQN SYSTEM Henry R. Butler, Verona,N. J., assignor to Wired Radio, Inc., New York, N. Y., a corporation ofDelaware Application January 28, 1939, Serial No. 253,301

8 Claims.

This invention relates to receiving systems for supplying radiofrequency signal energy to a number of receivers and particularly tosuch a system covering the broadcast band of frequencies and comprisinga common antenna for all receivers in one or more buildings or arestricted area.

The principal object of the invention is to provide local radiofrequency signals for selective reception by ordinary receivers withintheir tuning range and without interfering with their normal selectivereception of space radio signals.

Another object is to improve common antenna systems so as to supplystrong, uniform signals from broadcasting stations which are weaklyreceived, as well as from stations strongly received.

Other and related objects will be apparent from the followingdescription in connection with the accompanying drawing in which:

Fig. 1 is a diagram of a preferred embodiment of the invention; and

Figs. 2 and 3 illustrate modified arrangements for distributing localand space radio signals to many receivers according to the invention.

Referring to Fig. 1, an antenna 5 for receiving space radio signals isgrounded at 6 through primary I of a radio frequency transformer, thesecondary 8 of which is connected to a radio frequency transmission lineIll.- The other end of the transmission line is connected to primary llof another radio frequency transformer which has a secondary l2connected to a wide-range, radio frequency amplifier l3. One end ofsecondary l2 may be connected to ground as at H, and groundedelectrostatic shields l5 may be disposed between windings l and 8, andII and 12, respectively. A plurality of tunable circuits or wave traps,such as Ilia, lGb, I80, lid, each comprising capacity C,

inductance I and adjustable resistance R, are connected across thesecondary l2 and the input of amplifier l3.

The output ll of amplifier I3 is connected to a distributing system I8for carrying the amplified signals to each radio receiver 20a, 20b, 20c,20d, etc. within the building or area to be supplied from antenna 5.Coupling transformers l9 may be provided to prevent interaction amongthe receivers. Each transformer l9 preferably comprises a primary 2|connected to system l8 and a grounded secondary 22 connected to areceiver. A grounded electrostatic shield 23 may be disposed between theprimary and secondary windings. While only four receivers are shown, itis to be understood that there may be several hundred or severalthousand receivers connected to the distributing system.

One or more local transmitters 25, 26 are connected to the amplifieroutput I! through resistance networks 21 and 28, respectively.Transmitters 25 and preferably are located near amplifier I3 and withinthe building containing the receivers, each said transmitter comprisingthe usual radio frequency oscillator and audio frequency modulatorcircuits and tubes. The output power of the transmitters may be low andpreferably is suificient to give a signal level at I! about equal to themaximum output of amplifier l3. The source of modulation energy ,for thetransmitters may be local as indicated at 30, which may be a microphone,phonograph pick-up or other device for supplying audio frequencymodulations to transmitter 25. Alternatively, the modulation energy maybe received from a distant point over a telephone line 3|, such as shownconnected to transmitter 26.

Another arrangement, if wired radio is available, is to couple afrequency multiplier or converter 32 to a power line 33 on which wiredradio signals have been impressed at a distant point. The coupling meansmay comprise condensers 34. The output of the frequency multiplierpasses through a resistance network 35 which is connected in parallelwith the networks 21 and 28.

The transmitters 25, 2B and frequency multiplier 32, with theirassociated apparatus, may be employed separately or in combination asone or more sources of local signals which are added to the spacesignals collected by antenna 5.

In the drawing, an ellipse surrounding a pair of wires (such as ill orl8) indicates that they may be shielded or concentric.

The operation of the system shown in Fig. 1 is as follows:

Space radio signals at various frequencies are collected by the antenna5 and carried to the individual receivers 20 a to d, etc. by thetransmission line It) and distributing system l8 in a manner known inthe art. The receivers are the usual type having arrangements to selectany carrier within their tuning range and to reproduce the modulationscarried thereby.

In accordance with one feature of the invention, amplifier l3 increasesthe strength of weakly received signals to such a level that themodulations may be reproduced with ample volume by moderately sensitivereceivers. Inasmuch as only one amplifier is required for the entireinstallation, it may be of very high quality and as sensitive asdesired, thereby saving the expense of providing such quality andsensitivity in each of a large number of receivers. In order to avoidunnecessary amplification of the signal received from a nearby or a highpower broadcasting station, one of the wave traps, for instance 5a, istuned to the carrier frequency of such station by means of variablecapacity C and the degree of attenuation of such signal is adjusted byvariable resistance R. Certain of the other wave traps may be tuned toother strong broadcasting stations so that approximately uniform signalstrength for all space radio signals will be obtained at the output I!of amplifier [3. Such multiple arrangement of wave traps may be calledan equalizer.

With the present allocation of broadcasting frequencies there are, inany locality, several frequencies for which the assigned stations areeither too far away or are of too low power to be received by ordinaryradio sets. In accordance with the principal object of the invention,such frequencies are selected for the local sources 25, 26 and 32. Thefrequency of source 32 should be a multiple of the wired radio frequencyreceived over line 33, for instance, 550 kilocycles which is theeleventh harmonic of a. 50 kilocycle wired radio signal. In some cases,the frequency selected for a local source may be the same as thefrequency of a broadcasting station which is not received satisfactorilybut nevertheless produces a beat note by heterodyning with the localfrequency. In such event one of the wave traps, such as lGd, is tuned tosuch frequency and its resistance R made zero, whereby the broadcastsignal is short-circuited before it reaches amplifier l3 and the beatnote is thus eliminated.

The radio frequency oscillations generated by sources and 26 aremodulated by audio frequencies representing programs from modulationsource 30 and telephone line 3!. The wired radio oscillations receivedover power line 33 are already modulated so it is necessary only to stepup their frequency by the multiplier or converter 32. It should beunderstood, however, that all the local sources may be alike, except asto frequency, and may be any of the three types illustrated in Fig. 1 orof other known types. The modulated outputs of sources 25, 26 and 32 areparalleled at I! with the output of amplifier l3. In this mannerprograms are made available at points on the dials of receivers 20a to20d which otherwise would not be used. Such local programs can be ofvery high quality and are not subject to fading or other disturbinginfluences, inasmuch as they are not transmitted through space, butinstead are fed directly into the distributing system IS.

The quality of local programs may be further improved by arranging thesources 25, 26 and 32 to deliver one side band only. For example,assuming that receivers 20 have a pass-band width of 8,000 cycles andthat they receive the usual double side band signals, the audiofrequency output would be cut off at 4,000 cycles. However, with singleside band transmission from local sources 25, 26 and 32, the full widthof 8,000 cycles would be available for one side band and therefore theaudio frequency cut-off would be raised to 8,000 cycles, therebyproviding higher quality programs from the local transmitters.

The function of the resistance networks 21, 28 and 35 is to preventinteraction or feed-back among the transmitters 25, 26, 32 and amplifierI3. Inasmuch as the signal level required at III is very small, suchresistance networks may pass as little as 10% of the transmitter outputsand still provide ample signal strength, even though the transmitterscontain low power radio tubes.

Fig. 2 shows a modified arrangement for distributing the output ofamplifier l3 when there are a large number of connected receivers. Inthis modification, the output I! of the amplifier is connected toprimary of a main transformer, the secondary 4| of which is connected inparallel to primaries 42, 43 and 44 of a number of auxiliarytransformers. Each auxiliary transformer has multiple secondaries, 45,46 and 41, the respective sections of which may be connected toindividual receivers. If desired, however, each section of secondaries45, 46 and 41 may be connected to the primaries of additional auxiliarytransformers having multiple secondaries connected individually to therespective receivers. The degree of sub-division may be carried as faras necessary to provide most economically for the number of receivers inthe building.

Fig. 2 also shows a modified arrangement for feeding in the local radiosignals from a single transmitter 48 by connecting the transmitter inparallel with the amplifier output ll through suitable resistance 50 and5|, in the connecting leads.

Fig. 3 shows another modification wherein the output of amplifier I3 ismade to have very low impedance, such as by transformer 52 having a lowimpedance secondary winding. The proper impedance depends upon thenumber of branch transmission lines to receivers and on thecharacteristic impedance of each line. For instance, if there were onlyone line with one receiver connected thereto the output impedance oftransformer 52 might be 70 ohms, whereas if there are 700 branch lines,each connected to a receiver, the output impedance would beapproximately 0.1 ohm. Such impedance does not depend upon how many ofthe connected receivers happen to be in operation. In a low impedancesystem the output of the local transmitter 53 should also have a lowimpedance and may then be directly connected to the output oftransformer 52 and to the distributing system 18a. This system maycomprise transformers 54, 55, 56, 51, etc., all connected in parallel.Each transformer may supply one floor or section of a building byconnecting their secondaries to individual transformers in the receiverson that floor or section, or by interposing auxiliary transformers as inFig. 2.

While a preferred embodiment and certain modifications have beendescribed above and illustrated in the accompanying drawing, it is to beunderstood that various changes may be made without departing from thespirit and scope of the invention.

What I claim as new and original to be secured by Letters Patent of theUnited States is:

1. In combination, an antenna for receiving space radio signals,throughout a given frequency range, means connected to said antenna fordistributing the signals to several radio receivers at the frequenciesreceived, a local transmitter coupled directly with said distributingmeans for supplying additional signals to said receivers within thegiven frequency range, and means connected between said antenna and saiddistributing means for eliminating received signals having substantiallythe frequency of said local transmitter and for preventing radiation ofsaid additional signas from the antenna.

2. In combination, an antenna for receiving space radio signalsthroughout a given frequency range, means connected to said antenna foramplifying said signals, means for distributing the amplified signals toseveral radio receivers at the frequencies received, each receiver beingindividually selective to desired signals, a local radio fre- Examinquency transmitter coupled between said amplifying means and saiddistributing means for supplying additional signals to said receiverswithin the given frequency range, and a wave trap connected between saidantenna and said amplifying means, said wave trap being tuned to thefrequency of said local transmitter.

3. In a system for collecting space radio programs transmitted onassigned carrier frequencies and for distributing the same withoutchange of frequency to a multiplicity of connected radio receivers, themethod which comprises, feeding an additional program directly into thedistributing system at a carrier frequency such that space radioprograms assigned. to that frequency are not receivable, making theenergy level of the fed-in program comparable to the energy level of thestrongest carrier among the received space radio programs, andeliminating from the collecting system any extraneous signals and statichaving substantially the frequency of the fed-in carrier.

4. In a system for collecting space radio programs transmitted onassigned carrier frequencies and for distributing the same withoutchange of frequency to a multiplicity of connected radio receivers, themethod which comprises trapping out a weak undesired program andsubstituting therefor a local program on substantially the same carrierfrequency by feeding said local program directly into the distributingsystem at an energy level about equal to the strongest of the receivedprograms.

5. The combination defined by claim 1 in which said local transmitter isarranged to suppress one side band and to deliver single side bandsignals to said distributing means.

6. The combination defined by claim 1, and an equalizer also connectedbetween said antenna and said distributing means, said equalizercomprising a plurality of tuned circuits and adjustable resistances formaking the energy levels of the received space radio signalsapproximately uniform.

7. A radio reception system for a restricted area containing amultiplicity of radio receivers, said system comprising, an antenna forcollecting space radio signals, circuit means connecting said antenna tosaid receivers, an untuned radio frequency amplifier forming part ofsaid circuit means, a plurality of sources of local radio frequencysignals connected to the output of said amplifier, at least one wavetrap connected across the input of said amplifier and tuned to thefrequency of one said source, and at least one additional wave trapconnected across the input of said amplifier and tuned to a strong spaceradio signal collected by said antenna.

8. A radio reception system as defined by claim '7 in which at least oneof said local sources produces radio frequency signals in the form of acarrier with single side band.

HENRY R. BUTLER.

